Ecological Soil Screening Level Guidance Released

The Rocky Mountain Arsenal National Wildlife Refuge will provide protected habitat for hundreds of mule deer, as well as black-tailed prairie dogs, migrating waterfowl, and eagles.

The Office of Solid Waste and Emergency Response released the final version of Guidance for Developing Ecological Soil Screening Levels (Eco-SSLs) this past November. The guidance is the result of collaboration between federal and state agencies, industry, consulting, research institutes, and universities through an Office of Superfund Remediation and Technology Innovation workgroup. Prior to releasing the guidance, the workgroup consulted the EPA's Science Advisory Board for commentary, and the draft guidance underwent a formal peer review at a public workshop.

Eco-SSLs are contaminant concentration levels that are protective of ecological receptors (e.g., mammals, birds, or plants) that might have contact with the soil, directly or indirectly. The need to establish Eco-SSLs and document the derivation process arose from the lack of peer-reviewed soil screening values and from the desire to streamline the ecological risk assessment (ERA) process at hazardous waste sites. The Eco-SSLs will make the ERA process more efficient and cost-effective by reducing redundancy, increasing consistency, and decreasing potential oversight. The derivation process is outlined in the guidance, allowing other parties to develop additional Eco-SSLs for contaminants for which Eco-SSLs have not been established.

In setting out to draft the guidance, the workgroup established a list of 24 contaminants comprised of 17 metals (including arsenic, chromium, and lead) and seven organics (including polycyclic aromatic hydrocarbons). EPA created the contaminant list using contaminants of concern reported in recent Records of Decision for National Priority List sites and contaminants recommended for inclusion by the EPA regional Biological Technical Assistance Group Coordinators. If contaminants of concern are present in soil at concentrations above the derived Eco-SSL, the environment may be adversely affected, and the soil contaminants may require further evaluation in the baseline ecological risk assessment. The Eco-SSLs can be used to make the screening-level risk calculation for a Superfund Ecological Risk Assessment. They are not intended to be used as cleanup levels nor is it appropriate to use or modify the Eco-SSLs as cleanup standards.

Eco-SSLs have not been established for all of the contaminants. To date, interim Eco-SSLs and documentation are available for aluminum, antimony, barium, beryllium, cadmium, cobalt, dieldrin, iron, and lead.